Enable post-ruby-install hook

action.yml

@@ -30,6 +30,11 @@ inputs:
       to invalidate the cache.
     required: false
     default: '0'
+  post-ruby-install:
+    description: |
+      Execute a shell command after installing Ruby but before installing non-default Bundler gem.
+      Ignored if `input.bundler` is set to 'none'.
+    required: false
 outputs:
   ruby-prefix:
     description: 'The prefix of the installed ruby'

index.js

@@ -2,6 +2,7 @@ const os = require('os')
 const fs = require('fs')
 const path = require('path')
 const core = require('@actions/core')
+const exec = require('@actions/exec')
 const common = require('./common')
 const bundler = require('./bundler')
 
@@ -13,6 +14,7 @@ const inputDefaults = {
   'bundler-cache': 'true',
   'working-directory': '.',
   'cache-version': bundler.DEFAULT_CACHE_VERSION,
+  'post-ruby-install': null,
 }
 
 // entry point when this action is run on its own
@@ -61,6 +63,14 @@ export async function setupRuby(options = {}) {
   }
 
   if (inputs['bundler'] !== 'none') {
+    // Similar to 'afterSetupPathHook' but for use within the Runner environment directly by end-user.
+    // If Bundler isn't being installed, this hook is redundant because the user is then free to execute
+    // their script in a separate `job.step`.
+    if (inputs['post-ruby-install']) {
+      await common.measure('Running Post Ruby Install Hook', async () =>
+        await exec.exec(inputs['post-ruby-install']))
+    }
+
     const [gemfile, lockFile] = bundler.detectGemfiles()
 
     const bundlerVersion = await common.measure('Installing Bundler', async () =>